The present invention relates to a door closer of the kind that is used to control the movement of a door from an open position to a closed position.
Door closers are conventionally fitted to a door or a door frame and generally comprise a mechanism for storing energy which is typically in the form of a spring. Energy is stored by the spring during opening of the door and is released to effect automatic closure of the door.
In one common type of door closer a rotary spindle for coupling to the door rotates with opening movement of the door. The spindle is coupled a transmission mechanism that converts the rotational movement into rectilinear reciprocation of a piston in a first direction within an elongate door closer housing. The spring biases the piston in an opposite second direction to urge the door to the closed position and the speed of movement of the door between the open and closed positions is controlled by the flow of hydraulic fluid from one side of the piston to the other via passages for the restricted flow of fluid. In one example the transmission mechanism is a pinion that rotates with the spindle and drives a rack in translation, the rack being connected to the piston. In other example, a cam is coupled to the spindle and acts directly or indirectly on part of the piston.
Door closers of the kind described require the spring to apply a predetermined force that is relatively high to resist opening of the door so as to meet fire regulations. Once the initial opening travel of the door is complete the resisting force need not be so high. At the end of the opening movement it is desirable to have a slight rise in the force to give a detent feeling for the user.
A conventional spring has a linear spring force characteristic during compression as indicated in FIG. 1. The spring stress is increased as the door opens to deliver the high forces and this can lead to premature spring failure. Mechanisms such as a cam or kinematic linkage are usually incorporated into the closer to achieve modify the force such that it more closely approximates to a desired force profile. The introduction of such a mechanism reduces the overall efficiency of the closer and therefore larger spring forces are necessary to achieve the desired output force. This generally means that larger springs and mechanisms have to be accommodated and the door closer housing is correspondingly large.
It is one object of the present invention to obviate or mitigate at least one of the aforesaid disadvantages. It is also an object of the present invention to provide for an improved or alternative door closer.
According to a first aspect of the present invention there is provided a door closer for coupling to a door comprising a housing and a drive member disposed in the housing for movement relative to the housing as the door moves between open and closed positions, at least one first magnetic means coupled to the drive member, at least one second magnetic means coupled to the housing, the at least one first and second magnetic means arranged in the housing with their opposite poles facing one another such that there is a magnetic force of attraction between them, whereby relative movement of the housing and the drive member effects relative movement of the at least one first and second magnetic means between proximal and distal positions, the at least one first and second magnetic means being biased to the proximal position by the magnetic force of attraction, at least one of the first and second magnetic means being a permanent magnet.
In use the magnetic force of attraction is exploited to provide a force that biases the door to the closed position. By using magnets this force can be relatively high for a short distance of movement of the door and the magnets, the force dropping off relatively rapidly as the magnets move to the distal position. The force also operates to provide a resistance to opening of the door.
The magnetic means may be a permanent magnet, an electromagnet or a magnetic material (such as, for example, a ferromagnetic material) that defines a pole piece for attraction to an opposite magnetic pole.
The door closer mechanism is thus simple and compact allowing it to be fitted into relatively confined spaces, particularly as large springs are not required to apply the large forced required to generate the large torque required to close the door. In particular it may be concealed in a rebate in the door or door frame.